Cap, Body Material Black Malleable Iron, Class 150, Pipe Size 4 In., Connection Type FNPT, Max. Pressure 300 psi@150 Degrees F, Saturated Steam Pressure 150 psi, Temp. Range -20 Degrees to 366 Degrees F, Standards ASTM A-197, ASTM A47, ASME B16.3 and B16.4, UL Listed, FM Approved
So I think the Grainger Approved Cap,4 In.,FNPT Model: 2WU81 was okey, but it's not as impressive as I hooped. Price can be lower too.